Conventionally, in the field of power electronics, a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) has been used as a switching element having a high-speed switching function. As a structure of a power MOSFET, a super junction structure can be exemplified.
In the super junction structure, an n-type layer and a p-type layer are alternately formed in a conductive layer that connects a source and a drain. In the super junction structure, a depletion layer is formed in an interface between the n-type layer and the p-type layer. Accordingly, between the source and the drain, an electric field is formed not only in a direction from the source to the drain, but also in a direction from the n-type layer to the p-type layer. As a result, the electric field between the source and the drain does not concentrate on a certain part in the conductive layer. Therefore, the super junction structure can provide high voltage resistance performance.
As a method of producing a semiconductor substrate used for forming the super junction structure, a method of forming a trench in an epitaxial layer and forming a plurality of epitaxial layers in the trench thus formed is proposed (for example, refer to Patent Documents 1 and 2).
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2005-294711
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2005-317905